Flight model congratulations for the F-16!

[85th_Maverick]

Hello ED!

 

Very good job with the F-16!

 

Even if ED has used the NASA's free document "TP 1538" which contains most of the important real aerodynamic data for the F-16 or not, one doesn't have to be a real pilot in order to be good at identifying right from wrong through experience and knowledge. The pitching moments versus AoA and versus elevators deflections at different AoA are right! The rolling moments versus AoA+Beta for various flaperons+elevons as well as rudder deflections (up to the limit which the ARI allows you to deflect the rudder outside of the FBW's inputs) are all right! And most important, the maximum lift coefficient and lift and drag to AoA are spot on, not exaggerated or underrated.

 

From the aerodynamic forces simulations all around the AoA and Beta angles, this plane is almost 100% nailed and I'm very pleased with what you have achieved through it.:thumbup: From how I see it, for how well it's flight model is done compared to the other jet fighter aircraft, it's not expensive!

 

There is only one thing left to be done, which is the addition of the missing rolling moments versus high Beta for different angles at which the wings meet the airflow.

 

For example, if you climb at a 80 deg. of pitch up and let the plane decelerate with idle throttle, up to say 200KIAS, then roll right to any bank angle between 20 to 95 degrees and simply let the plane fall with it's right wing towards the ground, normally the plane should start getting a leftward rolling moment, higher or lower depending on actual angle between the airflow vector and the wings planes (the F-16 has a small anhedral). I guess that due to the lack of aero data, the sim cannot model any rolling moments from those conditions! This same thing happens with the F-18 as well as the plane can literally fly with one wing forwards at some crazy 50-90 degrees of beta and no matter how the airflow attacks the leading wing, there is no roll occurring. I wish that sooner or later this gap will also be filled for these three fighters. Most other planes have this effect nicely simulated, but these 3 don't!

 

Besides the missing high beta rolling moments, the F-16 is one of the finest simulated in DCS!

 

Thank you!

Edited May 28, 2020 by 85th_Maverick

[Aluminum Donkey]

It's entirely possible that the apparent lack of yaw-roll coupling is due to the FBW system correcting for it.

 

No roll input from the stick? No roll. The control surfaces are moved automatically to prevent the uncommanded roll.

 

You'd have to ask someone who's flown the real deal. Airplanes generally do have yaw-roll aerodynamic coupling, but it won't show up when flying it if the control system is designed to prevent it, which might be the case with the F-16. Same thing goes with a sudden crosswind gust on landing--the plane won't roll due to sideslip if the control system won't let it.

 

AD

[85th_Maverick]

It's entirely possible that the apparent lack of yaw-roll coupling is due to the FBW system correcting for it.

 

No roll input from the stick? No roll. The control surfaces are moved automatically to prevent the uncommanded roll.

 

You'd have to ask someone who's flown the real deal. Airplanes generally do have yaw-roll aerodynamic coupling, but it won't show up when flying it if the control system is designed to prevent it, which might be the case with the F-16. Same thing goes with a sudden crosswind gust on landing--the plane won't roll due to sideslip if the control system won't let it.

 

AD

 

No, it's zero possible that the roll control surfaces (directly commanded or by the FBW) have any effect at those angles, especially in roll! Maybe I've forgotten to say that with the ailerons at zero or at whatever deflection there are simply no rolling moments taking place above some Beta (side slip angle) and AoA combination.

 

Don't mix what the flight controls system logics do and what the aerodynamic effects on the whole plane including it's surfaces do in a way in which you may consider one taking place because of the other, because above a certain limit, only the developing aerodynamic effects become primary!

 

For instance, the FBW will try to prevent (as well as it can) the AoA or Beta from exceeding a given value based on angular rates or different input combinations, but..., once past the departing limit, the flight controls surfaces can't help the aerodynamic forces, hence moments effects that continue to evolve no matter how much those controls would deflect. From there on, the aerodynamic physics follow their laws. It's similar to having your car skidding at a 90 deg angle! Would it matter how you steer your front wheels (considering that your rear wheels are spinning at a similar rate as the front, to not vary the grip)? The difference would be just zero!

 

Do you think that at 90 Beta (such as the case that I've talked about earlier as you simply fall straight on one wing) with the airflow attacking your leading wing from above or below, will the flight controls have any effect? Furthermore, the ailerons and elevons are going to be exactly parallel with the airflow (the anhedral of the elevons will indeed generate a very slight pitch down (not towards the Earth), but still with zero roll effects), so no effect would occur on them even if you'd deflect them at 90 deg. As for the rudder, yes, that's the only thing that will increase or decrease the yawing moment that tends to reduce the Beta to a trim value, as the rudder deflections are now mostly varying the drag, not the lift on the fin.

 

The aero roll due to Beta are simply absent above some combinations with the AoA and the same goes with the F-18.

Edited June 12, 2020 by 85th_Maverick

[MROK73]

"You'd have to ask someone who's flown the real deal"

If he did, the answer would be "not close enough". Specially the "feeling" of the FLCS, and rolling rates (completely off). The numbers maybe the ones on paper, but airborne everything is screwed.

[Dee-Jay]

... among other things ... roll rate in CATIII is indeed currently about 1/2 of what it should.

[Majik]

... among other things ... roll rate in CATIII is indeed currently about 1/2 of what it should.

 

 

One of those other things is the AOA limit with gear down, isn't it? Because this thing just won't turn in on base and final when CATIII. Kunsan tower wouldn't be happy with me if I couldn't make the runway like this everytime ;)

[85th_Maverick]

Guys..., your answers have nothing to do with what I'm talking about! I'm talking about rolling moments generated by high Beta angles at very low AoAs, aerodynamic angles at which the flight controls have almost zero effect, the resulting wing rocking and momentary roll effects that should take place just due to the lift difference between one wing and another at those angles..., effects which are completely non-existent, what a heck is so hard for you to understand?

 

For the sake of your FBW (which again, has nothing to do with the subject here), take the JF-17 which is pretty comparable to the F-16 from aerodynamics and flight dynamics point of view or even any other fighter, including FC3. Except for the F-16 and F-18, all other aircraft exhibit more or less correct uncommanded roll-off effects at any Beta and AoA combination. I say more or less because airplanes like the Su-25, L-39, MIG-19 and MIG-21 don't correctly reverse the rolling moments to rudder input above a certain low negative AoA with zero ailerons input (a different story), but at least the rest of the airplanes in DCS show somewhat natural rolling motions at very high Beta and low AoA.

 

Here's a good example of what I'm talking about and hopefully you'll get what I'm talking about:

 

 

See that sharp throw-off in roll? That's one example. You can't see this with the DCS F-18 and F-16. Every airplane exhibits this! This is not something specific to X plane, but to any plane.

 

Here's another high beta low alpha which throws the plane into a momentary roll until both wings lift gets even (when Beta gets momentarily through zero to make both wings lift close to equal):

Just make the DCS F-18 do that nice roll-flip and you'll find out!

Edited June 12, 2020 by 85th_Maverick
Deleted a repetition

[85th_Maverick]

"You'd have to ask someone who's flown the real deal"

If he did, the answer would be "not close enough". Specially the "feeling" of the FLCS, and rolling rates (completely off). The numbers maybe the ones on paper, but airborne everything is screwed.

There are videos talking about these effects with both the F-16, F-18, whatever airplane gets at those high Beta low AoA angles. Only a few pilots get to test such conditions and those are test pilots. If you find me one that can talk about this and probably he'll make you understand that I'm right, I'll be waiting!

 

I'm not trying to make a fuss out of this small gap, after all, I say again, this is among the best ever modeled in DCS, just behind the JF-17 which truly nailed it!

[Dee-Jay]

I m not engineer, I am a simple driver. (not F-16 though ...)

I won't fight into your domain of expertise. No doubt you are much more educated than I am about equations and math. :)

 

your answers have nothing to do with what I'm talking about! I'm talking about rolling moments generated by high Beta angles at very low AoAs,

I think I see what you mean: You are speaking about FM while we are speaking about FLCS. Am I correct?

[Hummingbird]

The instantanous load factor/rates are still not correct, and neither is G/pitch onset rates.

 

So the FM still has some ways to go.